Views: 0 Author: Site Editor Publish Time: 2025-06-24 Origin: Site
When working with ceramics, the quality of your kiln furniture is just as crucial as the clay and glazes you use. Kiln furniture, which includes shelves, posts, and setters, plays a vital role in how your pieces fire and ultimately how they turn out. The right kiln furniture can enhance energy efficiency, improve firing results, and ensure the longevity of your kiln. This comprehensive guide will delve into the properties of various kiln furniture materials, helping you choose what will work best in your studio.
Before diving into the specifics of kiln furniture, it’s essential to understand some key terms that will help clarify your choices.
Cordierite is a low-expansion magnesium-aluminum-silicate refractory material formed by heating a mixture of talc, clay, and mullite to about 2462°F (1350°C). Its low coefficient of thermal expansion (CTE) makes it less prone to cracking under temperature changes, making it a popular choice for many ceramic artists.
CTE refers to how much a material expands or contracts with temperature changes, measured as length per unit length per degree of temperature change. A lower CTE indicates that a material is less likely to suffer thermal shock when subjected to rapid temperature fluctuations.
Mullite is another aluminum-silicate refractory formed by heating specific clays to temperatures above 2192°F (1200°C). It has excellent mechanical strength and thermal stability, making it suitable for high-temperature applications.
In ceramics, a refractory material is one that can withstand high temperatures, typically over 1000°F (538°C), without losing its integrity. The choice of refractory materials significantly impacts the performance and longevity of kiln furniture.
Silicon carbide is an extremely hard compound made by melting silica and carbon at temperatures exceeding 2732°F (1500°C). SiC is valued for its strength and high-temperature resistance, but it also poses risks in electric kilns due to its electrical conductivity.
Thermal shock occurs when a ceramic material experiences a rapid change in temperature, leading to cracking or breaking. Understanding thermal shock is crucial when selecting kiln furniture, as it can affect the durability and reliability of your shelves and supports.
The first thing to know about refractory kiln furniture is that not all refractories are created equal. Key factors to consider include composition, flexural strength, and maximum working temperature.
While refractory fiber and soft brick are typically used for insulation in kilns, kiln shelves and furniture are made from much denser refractories. These materials must withstand the weight of your ware, the heat of the firing process, and the potential for thermal shock. Selecting the appropriate material can significantly affect the efficiency of your kiln and the quality of your finished pieces.
Mullite is made from a blend of alumina and clay, with a typical composition of about 68% alumina and 32% silica. It provides excellent strength and thermal stability, making it suitable for various firing applications. However, mullite shelves and furniture are often less available than those made from cordierite.
Cordierite shelves are often the most cost-effective option for many studios. Their composition includes a mix of talc, clay, alumina, and silica, with a pure form containing almost 14.8% magnesium oxide (MgO). Cordierite has the lowest CTE of common kiln shelf materials, making it less prone to thermal shock. However, its lower strength and maximum working temperature can be limiting factors, particularly in more demanding firing conditions.
Virginia ceramic artist and educator William Schran advises against using cordierite shelves in wood and salt/soda firings. The sodium vapors from these firing methods can significantly shorten the lifespan of cordierite.
Despite these limitations, cordierite is often the best choice for many electric kilns operating at lower temperatures. The lighter weight of cordierite shelves also translates to reduced energy costs, especially as energy prices rise. Cordierite-mullite shelves provide a balance of cost, strength, and thermal performance, making them a popular choice among ceramic artists.
Silicon carbide is ideal for making stronger kiln shelves and supports that can withstand higher temperatures. Its higher flexural strength allows for thinner, lighter shelves without sacrificing load-bearing capacity. This weight reduction contributes to better energy efficiency, as less energy is required to heat the shelves compared to thicker options.
However, SiC poses risks in electric kilns due to its electrical conductivity, which can lead to dangerous situations if not properly managed. Additionally, SiC has a higher CTE than cordierite, making it more susceptible to thermal shock. Therefore, while SiC offers excellent strength and durability, careful consideration is required when using it in electric kilns.
When selecting SiC shelves, quality matters. The ADVANCER line by Saint-Gobain is one of the highest-quality options available, featuring lightweight and dense SiC shelves with excellent thermal properties. These shelves come at a higher cost but offer long-term benefits, making them a worthwhile investment for serious ceramic artists.
When evaluating different materials for kiln shelves and supports, consider the following factors:
l Thickness and Weight: Cordierite-mullite shelves are often thicker to compensate for their lower strength, which can result in added weight. This can be a significant factor in energy consumption during firing. Thinner shelves made from stronger materials like SiC can reduce the overall weight of the kiln load, improving energy efficiency.
l Cost: On a first-cost basis, cordierite shelves tend to be the least expensive. However, investing in higher-quality SiC shelves can lead to better energy efficiency and lower overall costs in the long run. It’s essential to weigh the initial investment against potential long-term savings.
l Temperature Resistance: High-alumina cordierite shelves typically have a higher maximum working temperature compared to standard cordierite shelves. This makes them a better choice for high-temperature firings.
For those seeking the benefits of cordierite while reducing weight, consider Corelite shelves from RESCO Products, Inc. These shelves are engineered to combine cordierite-mullite materials with design modifications that enhance strength and reduce weight, making them suitable for higher-temperature applications (rated up to 2336°F or 1280°C). Corelite shelves provide an excellent balance of performance and cost, making them a smart choice for many ceramic studios.
To ensure the longevity of your kiln furniture, proper maintenance is key. Here are some essential tips:
All kiln shelves need a kiln wash applied to their top surfaces to prevent glazes from sticking. Kiln wash helps protect the surface of the shelves and makes cleanup easier after firing. If you regularly flip shelves to keep them flat, remember to clean off the top before applying wash to the other side. Regular maintenance of kiln wash can prolong the life of your shelves significantly.
Store kiln furniture in a dry location, away from moisture. Refractories can absorb water, leading to potential explosions during firing as trapped steam expands rapidly. If you’re unsure about moisture content, slowly heat the kiln up to the boiling point of water, ideally over four hours at temperatures below 190°F (88°C) to thoroughly dry the shelves. Proper storage and maintenance practices are vital to ensuring the longevity and performance of your kiln furniture.
Choosing the right kiln furniture is crucial for optimizing your ceramic firing process. With options ranging from cordierite and mullite to silicon carbide, each material offers distinct advantages and limitations that can impact your work. Understanding the properties of these materials will enable you to make informed decisions that suit your specific firing needs. Investing in the right kiln furniture not only enhances your ceramic creations but also promotes energy efficiency, ultimately benefiting your studio in the long run.
The selection of kiln furniture is not just about immediate costs; it’s also about the long-term performance and efficiency of your kiln. By considering the factors outlined in this guide, you can choose the best kiln furniture that meets your artistic and practical needs.
For further information and to explore quality kiln furniture options, visit Yufeng Refractory.
